.TH RX2 4
.UC
.SH NAME
rx2 \- RX211/RX02 floppy disk
.SH DESCRIPTION
Rx2? refers to an entire disk as a single sequentially addressed
file.  The physical disk sector size is 128 bytes for single
density and 256 bytes for double density.  The logical block
size is 1024 bytes.  Each diskette has 250 logical blocks in
single density and 500 logical blocks in double density.
The standard device names begin with ``rx2'' followed by
the drive number.
.PP
The size and density of the disks are specified as follows:
.PP
.nf
.ta .5i +\w'rx00  'u +\w'minor device  'u +\w'unit  'u
	disk	minor device	unit	density
	rx20	0	0	single
	rx21	1	1	single
	rx22	2	0	double
	rx23	3	1	double
.DT
.fi
.PP
The block files access the disk via the system's normal
buffering mechanism and may be read and written without regard to
physical disk records.  There is also a `raw' interface
which provides for direct transmission between the disk
and the user's read or write buffer.
A single read or write call results in exactly one I/O operation
and therefore raw I/O is considerably more efficient when
many words are transmitted.  The names of the raw files
conventionally begin with an extra `r.'
.PP
In raw I/O counts should be a multiple of 512 bytes (a disk sector).
Likewise
.I lseek
calls should specify a multiple of 512 bytes.
.SH FILES
.ta 2i
/dev/rx2[0-3]	block files
.br
/dev/rrx2[0-3]	raw files
.SH "SEE ALSO"
dvhp(4), hk(4), hp(4), hs(4), ml(4), rf(4), rk(4), rl(4), rm(4), rp(4), xp(4)
.SH DIAGNOSTICS
\fBrx2%d: hard error bn %d cs2=%b er=%b\fP.  An unrecoverable
error occured during transfer of the specified sector of the specified
disk partition.  The contents of the two error registers are also printed
in octal and symbolically with bits decoded.
The error was either unrecoverable, or a large number of retry attempts
could not recover the error.
.SH BUGS
In raw I/O
.I read
and
.IR write (2)
truncate file offsets to 512-byte block boundaries,
and
.I write
scribbles on the tail of incomplete blocks.
Thus,
in programs that are likely to access raw devices,
.I read, write
and
.IR lseek (2)
should always deal in 512-byte multiples.
.PP
DEC-standard error logging should be supported.
.PP
A program to analyze the logged error information (even in its
present reduced form) is needed.